Unify handling of compat and normal libs in class loader contexts.

Also, add tests for compatibility libraries in class loader context.

This CL separates special-case handling of compatibility libraries into
a "fixup" step that is done after class loader context is constructed by
Soong. This allows to handle compatibility libraries and normal
libraries uniformly, which should enable further simplification of class
loader context representation (in subsequent CLs).

Currently the only "fixup" step is removal of libraries from conditional
class loader context if they already are in unconditional context. This
check cannot be done at the time when the libraries are added to
conditional context, because the full uncoditional context is not yet
known at that time. Previously construction of unconditional context was
delayed, now it is no longer delayed and handled in the same way as
unconditional context, and the "fixup" does the filtering.

Test: lunch aosp_cf_x86_phone-userdebug && m
Bug: 132357300
Change-Id: Ie71e9fb2d3d529b5317cd84e09ab3c853017c349